Authentication bypass in GNU Inetutils telnetd grants access without a password

CVE-2026-24061 is a critical authentication bypass in GNU Inetutils telnetd. Improper handling of the "-f root" value in the USER environment variable allows an unauthenticated remote attacker to bypass authentication and gain unauthorised access, potentially with root privileges. Ubuntu recommends disabling telnet, applying available patches and reviewing systems for signs of historical compromise, as telnet remains inherently insecure and unsuitable for modern environments.

What this means for your organisation

Telnet should not be running, yet it is. The service turns up on legacy Linux servers, on network equipment and in industrial environments where something was configured long ago and never touched again. What makes this flaw serious is that it removes the last obstacle: the password. If you find telnet in your environment, it is not only a vulnerability to close but a sign that your inventory of exposed services is not good enough.

Berigo recommends

• Scan internal and external networks for open telnet ports and document every hit.
• Disable telnet and replace it with SSH rather than settling for applying the patch.
• Review logs on affected systems for logins that cannot be accounted for.
• Establish a recurring routine for mapping exposed services so forgotten equipment does not become a permanent blind spot.

Source

• ubuntu.com